Synthesis of highly emissive 1,8-diaryl anthracene derivatives and fabrication of their micro/nanostructures

Article abstract of DOI:10.1039/c5ra19564k

We report a new route for the synthesis of 1,8-diaryl anthracene derivatives (1-6) starting from anthraquinone. The reduction of 1,8-dichoroanthraquinone, followed by aryl-aryl coupling using modified Suzuki-Miyaura reaction conditions, furnished 1,8-diarylanthracene derivatives in a good yield. Detailed photophysical and electrochemical studies show that these anthracene derivatives emit in the blue region with a narrow FWHM and provide high quantum yields (upto 75%). The HOMO and LUMO energy levels of these compounds are in the ranges of -5.62 to 5.71 and 2.68-2.79 eV, respectively. Furthermore, anthracene derivative 5 was used for a surfactant assisted self assembling process to obtain micro/nanostructures. Compound 5 formed microplates in polyvinylpyrrolidone (PVP) and nanowires with an average diameter of ～290 nm in cetyltrimethylammonium bromide (CTAB). The absorption and emission properties of the micro/nanoassemblies of compound 5 showed a red shift of about 12 nm. It was also noticed that the emission intensity of 5 was retained even in the nanoassemblies, and was found to be comparable with that of the solution of 5 in organic solvents. DFT calculations suggest that multiple hydrogen bonding interactions are possible between two interacting monomers of 5. We believe that the possibility of H-bonding interactions in 5 is one of the factors that may aid the formation of micro/nanoassemblies. The blue emitting properties, compatible HOMO and LUMO energy levels, and highly blue emitting micro/nanoassemblies of these compounds make them suitable materials for organic light emitting devices (OLEDs).

Full text of DOI:10.1039/c5ra19564k

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Synthesis of Highly Emissive 1,8ꢀdiaryl Anthracene Derivatives and
Fabrication of their Micro/nanostructures
Neeraj Agarwal*, Manish Patil and Mahendra Patil
UMꢀDAE, Centre for Excellence in Basic Sciences, University of Mumbai, Kalina
campus, Santacruz (E), Mumbai 400098, India
Email: na@cbs.ac.in
Keywords: 1,8ꢀdiaryl anthracene, synthesis, quantum yield, nanoassemblies, Hꢀ
bonding interaction
Abstract
We report a new route for the synthesis of 1,8 Diarylꢀanthracene derivatives (1ꢀ6
)
starting form anthroquinone. The reduction of 1,8 dichoroanthraquinone followed by
arylꢀaryl coupling using modified SuzukiꢀMiyuara reaction conditions furnished 1,8
diaryl anthracene derivatives in the good yields. Detailed photophysical and
electrochemical studies show that these anthracene derivatives emit in the blue region
with a narrow FWHM and provide a high quantum yield (upto 75%). The HOMO and
LUMO energy levels of these compounds are in the range of ꢀ5.62 to 5.71 and 2.68 to
2.79 eV, respectively. Furthermore, anthracene derivative
5 was used for the surfactant
assisted self assembling process to obtain the micro/nano structures. Compound
5
showed microplates in the polyvinylpyrrolidone (PVP) and nonowires with an average
diameter of ~290 nm in the cetyl trimethylammonium bromide (CTAB). Absorption
and emission properties of micro/nano assemblies of compound
about 12 nm. It was also noticed that the emission intensity of
even in the nano assemblies and is found to be comparable with the solution of
5
showed red shift of
has been retained
in
5
5
organic solvents. The DFT calculations suggest that multiple hydrogen bonding
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interactions are possible between two interacting monomers of 5. We reckon that the
possibility of Hꢀbonding interactions in
5 is one of the factors which may helps in the
formation of micro/nanoꢀassemblies. The blue emitting properties, compatible HOMO
and LUMO energy levels, highly blue emitting micro/nano assemblies of these
compounds makes them suitable material for the organic light emitting devices
(OLED).
_________
Introduction
Anthracene derivatives have attracted a great deal of attention in the recent times
owing to their various chemical, photophysical and medical applications.1ꢀ3 For instances,
they have been frequently used as fluorescence probes, singlet oxygen acceptors, as well as in
optoelectronic devices including organic thinꢀfilm transistors, solar cells, upconversion of
energy using tripletꢀtriplet annihilation process etc.4ꢀ9 Moreover, anthracene derivatives
possessing a high fluorescence quantum yield and good chemical photo stability have found
applications in the organic light emitting devices (OLEDs).10 Recently, it has been shown that
triplet–triplet annihilation (or triplet fusion) and thermallyꢀactivated delayed fluorescence in
the anthracene based OLEDs led to a very high external quantum efficiency (16.5%).11,12
However, unsubstituted anthracene has a very low fluorescence quantum yield and it readily
crystallizes in thin film which limits their application in the solid state devices. Consequently,
several attempts were made to improve the emission and thin film properties of anthracene
derivatives. In particular, phenyl substitution at the 9 and 10 positions of anthracene is found
to be a successful protocol towards improving photophysical properties of the anthracene.13,14
Phenyl rings of diphenyl anthracene (DPA) are found to be out of the plane on the anthracene
core which causes a marginal bathochromic shift and also prevents crystallization of DPA in
2

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the thin film.14 It was demonstrated that film forming properties of DPA can be improved by
introducing the bulky arylꢀbased substituents at the ꢀ9,10 positions or other positions (2,6
position) of anthracene.15 While substitution at the 9,10ꢀpositions of anthracene is well
reported and studied in the literature, substitution at other positions of anthracene are rarely
explored. Recently, 2,6ꢀdiphenyl anthracene was reported using 2,6ꢀdihydroxy anthracene as
a starting material which was obtained by the reduction of 2,6ꢀdihydroxy anthraquinone
(Scheme 1a).16 Similarly, 1,8 diphenyl anthracene has been reported using reaction of phenyl
magnesium bromide with 1,8ꢀdichloroanthracene which was obtained by the reduction of 1,8ꢀ
dichloroanthraquinione.17 However, this method employs Grignard reagents which are not
easy to prepare and requires perfect anhydrous reaction conditions (Scheme 1b) and hence,
make it less practical. It is worthwhile to mention that the preparation of Grignard reagent has
limitation towards several organic functional groups. Alternatively, to synthesize aryl
substituted anthracene, the convenient approach is the arylꢀaryl bond formation using Suzukiꢀ
Miyaura, Stille or Negishi coupling reactions.18 Such coupling reactions requires 1,8ꢀ
haloanthracene derivatives which are difficult to synthesize, since 9,10 positions of
anthracene are more active towards halogenations. In this work, we have synthesized 1,8ꢀ
dichlroanthracene from readily available strating material 1,8ꢀdichloroanthraquinone. 1,8ꢀ
Dichlroanthracene is further subjected to the SuzikiꢀMiyaura coupling using 1,3ꢀBis(2,6ꢀ
Diisopropylphenyl)imidazolꢀ2ꢀylidene](3ꢀchloropyridyl)palladium(II) dichloride (PEPPSIꢀ
iPr)18h,i to obtain six different 1,8ꢀaryl substituted anthracene derivatives (1ꢀ6). The
substituents such as methoxy (3), acetyl (4) fluro (5) and trifluromethyl (6) on phenyl group
are expected to facilitate intermolecular hydrogen bonding interactions. Moreover, the
substitution at various positions of polycyclic aromatic systems helps in aggregates or
micro/nano assemblies formation which in turn, improves the optical properties of the
material.19 Lee et al. reported the selfꢀassembled nanoꢀribbons and nanoꢀrods by varying the
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solubility of DPA molecules in the solution.[20] More recently, surfactant assisted nanowires
and microrods of DPA molecules were synthesized and used in OLEDs and it was also
noticed that the nanowire is the best shape for the heterojunction light emitting devices.20
Hence, the surfactant assisted micro/ nanoꢀsized self assemblies formations of new
anthracene derivatives (1ꢀ6) are also attempted and successful attempts for 5 are reported in
this article.
Scheme 1.
Results and discussions
Typically, the SuzukiꢀMiyaura coupling reactions employs the reaction of bromo or
iodoꢀsubtituted aryl substrate with the aryl boronic acid in the presence of Pd0 and base to
produce diaryl derivatives.18a However, SuzukiꢀMiyaura coupling reaction is not efficient
with the chloroꢀsubstituted aryl substrate in the presence of conventional catalyst Pd(PPh3)4.
To overcome this problem, we have taken the advantage of recently reported SuzukiꢀMiyaura
coupling reaction with chloro aryl substrate in the presence of new catalyst, PdꢀPEPPSIꢀiPr.
Using this strategy, we have synthesized 1,8ꢀdiaryl anthracene derivatives (1ꢀ6) from
compound 7 as shown in Scheme 2. Compound 7 is obtained by reduction of commercially
available 1,8ꢀdichloro anthraquinone.17d Compound 7 is then, reacted with substituted aryl
boronic acid, Na2CO3, toluene, THF and water in the presence of catalytic amount of Pdꢀ
PEPPSIꢀiPr (5ꢀ7 mole %) at 850C for 16ꢀ18 h. Usual reaction work up and purification by
column chromatography afforded the 1,8ꢀ diaryl anthracene derivatives 1ꢀ6 as white or off
white solids (except 3,4 which are slightly yellow) in 52ꢀ77 % yields.
Scheme 2.
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All these compounds were identified using several spectroscopic techniques such as
1HꢀNMR, 13CꢀNMR, mass spectrometry etc. and their characterization data have been
1
summarized in the experimental section. Representative HꢀNMR of 1,8ꢀdi(4ꢀfluorophenyl)ꢀ
anthracene, 5 is shown in Figure 1. Singlet at 8.57 and 8.50 ppm were assigned for protons at
9ꢀ and 10ꢀpositions. Proton at 9ꢀposition of substituted anthracene is downfield shifted as
compared to unsubstituted anthracene may be because of the presence of electron
withdrawing nature of aryl group in the neighborhood. Doublet for two protons at 8.07 ppm
and triplet for two protons at 7.54 ppm were assigned for the protons at 4ꢀ and 3ꢀ positions
respectively. Protons at the 2ꢀpositions were appeared as doublet at 7.40 ppm. 4ꢀ
Fluorophenyl protons showed two different doublets for four protons each at 7.46 and 7.15
ppm. It can be noticed from Figure 1 that the signals for protons are slight broader
presumably because of Hꢀbonding (vide infra). Signals related to molecular mass ion is
observed in MALDI for compounds 1ꢀ6 (see supplimentary information) which further
confirm the formation of 1ꢀ6. All these compounds are fairly soluble in common organic
solvents. Melting points of these compounds are high.
Figure 1:
The UVꢀvisible absorption spectroscopic studies of 1ꢀ6 were carried out in toluene
(Figure 2) and in drop casted film (see supplimentary information). Toluene solution of 1
shows absorption maxima (λmax) at 395 nm and other high energy absorption peaks at 354
and 375 nm (πꢀπ* transition). Compounds 2ꢀ6 also showed the similar pattern in absorption
spectra with a marginal blue or red shift of 4ꢀ5 nm depending on the substituents. Drop casted
thin film absorption spectra showed slight broad peaks and a bathochromic shift of about 2ꢀ3
nm except in 5. Compound 3 and 5 showed a large bathochromic shift of 17 nm and 11 nm
respectively, which shows inter molecular interaction in the thin films. Similar trend was
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observed in the emission spectra having fluorescence maxima at 432 nm for 1 and 432 to 440
nm for compounds 2ꢀ6 (Figure 2). Fluorescence quantum yields of these anthracene
derivatives were calculated in the toluene using 9, 10ꢀdiphenyl anthracene (0.95 in ethanol) 13
as standard and have been summarized in table 1. Fluorescence life time data of these
compounds (1ꢀ6) recorded using TCSPC technique are provided in Table 1. Single
exponential fit was observed and spectra are given in the supplementary information.
Figure 2:
Table 1:
Compounds 1ꢀ6 were studied by cyclic voltammetry to get the insight on their
oxidation potentials which together with photophysical studies give information on
their HOMO and LUMO energy levels. Cyclic voltammetry and differential pulse
voltammetry were recorded in CH3CN at a scan rate of 100 mV/s using
tetrabutylammoniumhexafluorophosphate (TBAHP) as supporting electrolyte. In these
experimental conditions only oxidation waves were observed for 1ꢀ6 (except
reduction of these couldn't be seen. A comparison of first oxidation wave of
compounds 1ꢀ6 except is shown in Figure 3 and the data for them are presented in
3) and
3
Table 2. The 1,8ꢀdiaryl substituted anthracene are relatively difficult to oxidize
compared to 9,10ꢀdiphenylanthracene (Eox of DPA is lesser by 0.1 eV) which is
clearly evident from the data presented in Table 2.21 EHOMO of new anthracene
derivatives were calculated using oxidation peak potentials and using the internal
standard Fc/Fc+ value at 4.8 eV versus vacuum. ELUMO were calculated using the
EHOMO and optical band gap for the respective compounds obtained from onset of
absorption spectra in drop casted film. EHOMO and ELUMO of 1ꢀ6 were found ~ ꢀ5.6 eV
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and ꢀ2.7 eV. The HOMO and LUMO energy levels of ( 1ꢀ6) suggest that these
compounds can be used in OLEDs as blue emitter.
Figure 3:
Table 2:
Next, the surfactant assisted micro/nano self assemblies formations of 1ꢀ6 were
studied. Out of these anthracene derivatives, only
5
have provided wellꢀorganized nanoꢀ
micro/nano structures with
sized assemblies. Figure 4 shows the SEM images of the
5
different morphologies, which were obtained by the surfactantꢀassisted precipitation
method. Different surfactants such as PVP and CTAB were used in this procedure (details
are given in the experimental section). As shown in Figure 4 (A), discontinuous
rectangular plates were observed when
5 (in THF) added to the aqueous solution of PVP
with a vigorous stirring. The inset in Fig 4(A) shows magnified image of rectangular
plates with the smooth surface of different sizes. Variation in surfactants led to changes in
the morphologies of
5
. The CTAB assisted assembly formation of
5
in THF gave
(inset Figure
nanowires as shown in Figure 4(B). It can be noticed that nanowires of
5
4(B)) have virtually uniform diameter and shows continuous structures. The average
length and diameter of nanowires is found to be around 100 ꢁm and 290 nm, respectively.
We believe that the interꢀmolecular Hꢀbonding interactions in
5 facilitated by the presence
of terminal fluorine group on phenyl may be the reason for the nonoꢀsized assemblies
formations in 5.
Figure 4.
Micro/ nanostructures of 5 were studied with UVꢀvisible and emission spectroscopies.
UVꢀvis absorption showed redꢀshifted spectrum with a broad tail absorption in a longer
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wavelength region as shown in Figure 5. Absorption spectra of 5 in PVP and CTAB showed
18 nm red shift as compare to compound 5 in THF. Long tail absorption is assigned due to
scattering effect caused by micro/nano particles. The emission spectra of 5 and its assemblies
in PVP and CTAB showed similar trend as observed in UVꢀvis absorption. A bathochromic
shift of 10 nm and broad tail was observed in the emission spectra as well. These findings in
absorption and emission spectra further prove the formation of surfactant assisted micro/nano
sized assemblies.
Figure 5:
In order to identify the nature of non bonding interactions in the substituted
anthracenes, we performed computational investigations on the 1 and 5 using density
functional theory (DFT) methods. All calculations were performed using Gaussian 09 suite of
programmes.22 Several chemically intuitive guess structures of the dimer of 1 and 5 were
23
considered for the geometry optimization at the B3LYP/6ꢀ311G** level of theory
and
optimized structures were further identified as minima using harmonic force constant analysis
at the same level of theory. Only the lowestꢀenergy structures are reported in this paper.
Calculated interaction energies between two interacting monomers were corrected by the
counterpoise (CP) method.24
Substitution of fluoro on the phenyl substituted anthracene allows the possibility of Hꢀ
bonding interactions between two monomers. Consequently, the two monomers of 5 are
found to be closely placed in the optimized structures than the two monomers of 1. The
shortest interꢀatomic distance between two monomers of 5 is 2.45Ǻ (average) whereas, in the
case of 1, two monomers are separated by 3.63 Ǻ (Figure 6). Such Hꢀbonding interactions
also lead to the strong interactions between two monomers in 5. The calculated interaction
energies between two interacting monomers in 5 and 1 are ꢀ1.86 and ꢀ0.12 kcal/mol,
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respectively. Furthermore, to assign Hꢀbonding interactions in more than two units of 5, the
tetramer structure of 5 was optimized at the B3LYP/6ꢀ311G** level of theory. The optimized
structure of tetramer of 5 delineating multiple hydrogen bonding interactions between
interacting monomers is shown in figure 6. Our calculations evidently suggest that multiple
hydrogen bonding interactions are possible in 5 which may help in forming nanoꢀsized self
assemblies in the surfactant assisted precipitation method.[25]
Figure 6.
Conclusions
We have synthesized six anthracene derivatives having different aryl groups at the
1,8 positions of anthracene by applying SuzukiꢀMiyaura coupling reaction conditions
on the 1,8ꢀdichlroanthrace. Substitutions such as methoxy, acetyl, fluoro,
trifluoromethyl on the phenyl groups were expected to facilitate intermolecular
hydrogen bonding interactions. Photophysical characterizations of these derivatives
show that absorption and emission maxima of these derivatives are slightly
bathochromically shifted with reference to the DPA. Overall, these anthracene
derivatives emits in the blue region and show high extinction coefficients and
fluorescence quantum yields. Furthermore, the surfactant assisted micro/nanoꢀsized
assemblies formations of these anthracene derivatives were attempted. The nanoꢀsized
assemblies were successfully obtained only in the case of anthracene derivative
which have fluoro substituent on the phenyl groups. We have noticed that anthracene
derivative provides nanostructures with the different shapes in different surfactants.
In PVP/THF solution, rectangular microplates of were obtained whereas in
5
5
5
CTAB/THF solution, nanowires with uniform diameter were observed. Theoretical
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investigations on the anthracene derivative
possibilities for the intermolecular Hꢀbonding interactions in
interactions may favor the formation of micro/nanosized orderly structured as it is
observed in the case of . In all, we believe that the photophysical and electrochemical
parameters of the anthracene derivatives ( ) can be exploited in the organic light
5
have established the different
5
. Such Hꢀbonding
5
1ꢀ6
emitting devices. Currently, we are in the process of establishing the facility to explore
the possible applications of these compounds in OLEDs.
Experimental:
Chemicals
All general chemicals and solvents were procured from S D. Fine Chemicals, India and
SigmaꢀAldrich. Column chromatography was performed using silica gel obtained from Sisco
Research Laboratories, India. Tetrabutylammoniumhexafluorophosphate was purchased from
Aldrich and used without further purifications.
Instrumentation
1
13
The H and CꢀNMR (δ in parts per million) spectra were recorded using a Bruker
500 MHz spectrometer. Tetramethylsilane (TMS) was used as an internal reference
1
for recording HꢀNMR spectra (residual proton; δ = 7.26 ppm) in CDCl3. The MS
spectra were recorded on Bruker MALDIꢀTOF. UV–vis spectra were acquired at room
temperature on Shimadzu 1800. Fluorescence emission measurements were carried out
at room temperature using Horiba Fluoromax 4. For emission, compounds 1ꢀ6 were
excited at 380 nm. Cyclic voltammetry measurements were carried out using the
electrochemical analyzer (620D, CH Instruments Co.) at room temperature by utilizing
the threeꢀelectrode configuration consisting of Pt disc (working electrode), platinum
wire (auxiliary electrode), and standard calomel (reference electrode) electrodes. The
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experiments were done in dry acetonitrile with 0.1 M tetrabutylammoniumhexafluoro
phosphate as the supporting electrolyte. The sizes and shapes of the
micro/nanostructures were observed on a SEM (Quantaꢀ200 ESEM, FEI) at an
accelerating voltage of 5 kV.
Characterization.
1
1,8ꢀDichloro anthracene, 7: M.P.: 155
9.29 (s, 1H), 8.50 (s, 1H), 7.98 (d, 2H,
2H, J = 8.0 Hz).
°
C (lit.[20] 156ꢀ157
°
C) HꢀNMR (
δ
in ppm ):
J
= 8.5 Hz), 7.66 (d, 2H,
J
= 7.1 Hz), 7.44 (t,
General Procedure for the synthesis of anthracene derivatives 1–6:
A two necked round bottom flask was charged with compound 7 (1 eqv.), Na2CO3 (4ꢀ6
eqv.) and respective aryl boronic acid (2.4 eqv.) under Ar atmosphere. Mixture of toluene,
THF and water in equal volume ratio was added and temperature was raised to 60 °C. Pdꢀ
PEPPSIꢀiPr (5ꢀ7 mol%) was added and reaction was refluxed at 85 °C. After 12 h a fresh 2
mol % of catalyst was added, if required based on TLC analysis. Reaction mixture was
further stirred at 85 °C for total 16ꢀ18 h. Reaction mixture was cooled and extracted with
dichloromethane, organic layers were washed with brine and water. Solvents were removed
on rotary evaporator under vacuum; crude product obtained was purified by column
chromatography using hexane and ethyl acetate to afford the compounds 1ꢀ6 (~ 50ꢀ70%) as
white or off white solids.
1,8ꢀDiphenyl anthracene, 1: Mixture of
7 (0.12 g, 0.5 mmol), phenylboronic acid
(0.15 g, 1.2 mmol) and Na2CO3 (0.40 g, 4 mmol) in water/THF/toluene (1:1:1) 15 mL
were stirred under argon for 5 min and IPrꢀPEPPSI (0.05 g, 0.07 mmol) was added.
Reaction mixture was refluxed at 85 °C for 18 h. Silica gel column chromatography of
crude compound afforded compound
1
as white solid. Yield: (0.11 g, 69%). M.P.: 190
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°C. FTIR (KBr, cmꢀ1):
695, 603, 549. 1H NMR (500 MHz, CDCl3): δ 8.65 (s, 1H), 8.57 (s, 1H), 8.07 (d, 2H,
ν 3029, 2922, 1545, 1490, 1444, 1323, 1167, 1072, 879, 745,
J
= 8.5 Hz), 7.55 (t, 2H, J = 6.9 Hz), 7.52 (d, 4H, J = 7.3 Hz), 7.43 (m, 6H), 7.39 (d, 2H,
13
J
= 7.3 Hz) ppm. C NMR (500 MHz, CDCl3) δ 140.5, 140.4, 131.8, 129.9, 128.0,
127.6, 127.1, 126.7, 126.1, 125.2, 123.9 ppm. MALDIꢀTOF mass calcd. for C26H18
(M)+: 330.14; found: 330.55 (M+).
1,8ꢀDinaphthyl anthracene, 2: Mixture of
7 (0.12 g, 0.5 mmol), naphthylboronic
acid (0.21 g, 1.2 mmol) and Na2CO3 (0.40 g, 4 mmol) in water/THF/toluene (1:1:1) 15
mL were stirred under argon for 5 min and IPrꢀPEPPSI (0.05 g, 0.07 mmol) was
added. Reaction mixture was refluxed at 85 °C for 18 h. Silica gel column
chromatography of crude compound afforded compound
2
as white solid. Yield: (0.11
3031, 2660, 1550, 1494, 1442, 1326,
= 8.7 Hz), 8.14 (t, 2H, = 8.5
J = 8.1 Hz), 7.65 (t, 4H, J = 7.6 Hz), 7.56ꢀ7.57 (m, 2H), 7.41ꢀ7.46
g, 52%). M.P.: 208 °C. FTIR (KBr, cmꢀ1):
ν
1
1160. H NMR (500 MHz, CDCl3): δ 8.63 (d, 1H,
J
J
Hz), 7.85 (d, 1H,
(m, 4H), 7.30 (t, 1H,
(m, 2H), 7.20 (t, 1H,
J
J
= 8.0 Hz), 7.23ꢀ7.29 (m, 3H), 6.87 (t, 1H,
J = 7.5Hz), 7.04ꢀ7.09
= 7.5 Hz) ppm. 13C NMR (500 MHz, CDCl3): δ = 140.5, 131.8,
129.9, 128.1, 127.6, 127.1, 126.7, 126.1, 125.2, 123.9 ppm. MALDIꢀTOF mass calcd.
for C34H22 (M)+: 430.17; found: 429.95 (M+).
1,8ꢀDi (4ꢀmethoxyphenyl) anthracene, 3: Mixture of
7 (0.12 g, 0.5 mmol), 4ꢀ
methoxy phenylboronic acid (0.18 g, 1.2 mmol) and Na2CO3 (0.40 g, 4 mmol) in
water/THF/toluene (1:1:1) 15 mL were stirred under argon for 5 min and IPrꢀPEPPSI
(0.05 g, 0.07 mmol) was added. Reaction mixture was refluxed at 85 °C for 18 h.
Silica gel column chromatography of crude compound afforded compound
3 as
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slightly yellow solid (0.11 g, 58%). M.P.: above 220 °C. FTIR (ΚBr, ν 3036,
cmꢀ1):
2923, 1609, 1534, 1508, 1439, 1317, 1287, 1243, 1173, 1098, 1030, 885, 872, 828,
1
735, 555. H NMR (500 MHz, CDCl3): δ 8.67 (s, 1H), 8.54 (s, 1H), 8.03 (d, 2H,
J =
8.5 Hz), 7.54 (t, 2H,
7.00 (d, 4H, = 8.6 Hz), 3.90 (s, 6H, OCH3) ppm. MALDIꢀTOF mass calcd. for
J = 6.9 Hz), 7.46 (d, 4H, J = 8.5 Hz), 7.41 (d, 2H, J = 6.6 Hz),
J
C28H22O2 (M)+: 390.16; found: 389.84 (M+).
1,8ꢀDi (4ꢀactyl phenyl) anthracene, 4: Mixture of
7 (0.12 g, 0.5 mmol), 4ꢀacetyl
phenylboronic acid (0.196 g, 1.2 mmol) and Na2CO3 (0.40 g, 4 mmol) in
water/THF/toluene (1:1:1) 15 mL were stirred under argon for 5 min and IPrꢀPEPPSI
(0.05 g, 0.07 mmol) was added. Reaction mixture was refluxed at 85 °C for 18 h.
Silica gel column chromatography of crude compound afforded compound
4
as offꢀ
3038,
white (yellowish) solid. (77 %, 0.16 g). M.P.: 175 °C. FTIR (KBr
,
cmꢀ1):
ν
2916, 1670 (CO), 1552, 1455, 1424, 1400, 1312, 1356, 1262, 1167, 1091, 1016, 957,
1
828, 794, 732, 671, 593, 472. H NMR (500 MHz, CDCl3): δ 8.60 (s, 1H), 8.42 (s,
1H), 8.09 (d, 2H,
J
= 8.55 Hz), 8.03 (d, 2H, J = 8.1 Hz), 7.56ꢀ7.61 (m, 6H), 7.52 (m,
= 6.7 Hz), 2.67 (s, 6H, COCH3) ppm. HRMS mass calcd. for
2H), 7.47 (d, 2H,
J
C30H22O2 (M+H)+: 414.16; found: 384.42 (Mꢀ2CH3), 414.90 (M+).
1,8ꢀDi (4ꢀfluoro phenyl) anthracene, 5: Mixture of
7 (0.12 g, 0.5 mmol), 4ꢀfluoro
phenylboronic acid (0.17 g, 1.2 mmol) and Na2CO3 (0.40 g, 4 mmol) in
water/THF/toluene (1:1:1) 15 mL were stirred under argon for 5 min and IPrꢀPEPPSI
(0.05 g, 0.07 mmol) was added. Reaction mixture was refluxed at 85 °C for 18 h.
Silica gel column chromatography of crude compound afforded compound
5
as offꢀ
white solid. (0.12 g, 67%). M.P.: 204 °C. FTIR (KBr, cmꢀ1):
ν 3037, 2917, 1598,
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1
1503, 1443, 1462, 1326, 1218, 1157, 1093, 1015, 940, 906, 834, 791, 564, 525. H
NMR (500 MHz, CDCl3): δ 8.57 (s, 1H), 8.50 (s, 1H), 8.07 (d, 2H,
J
= 8.2 Hz), 7.54
13
(t, 2H, = 7.2 Hz), 7.39ꢀ7.45 (m, 6H), 7.13 (t, 4H, J = 8.3 Hz) ppm. C NMR (500
J
MHz, CDCl3): δ = 163.18, 161.22, 139.32, 136.29, 131.75, 131.40, 130.09, 127.75,
126.88, 126.26, 125.22, 123.35, 116.15, 115.97, 115.07, 107.46 ppm. MALDIꢀTOF
mass calcd. for C26H16F2 (M)+: 366.12; found: 365.71 (M+).
1,8ꢀDi (4ꢀtrifluoromethoxy phenyl) anthracene, 6: Mixture of
7 (0.12 g, 0.5 mmol),
4ꢀ (trifluoromethoxy) phenyl boronic acid (0.23 g, 1.2 mmol) and Na2CO3 (0.40 g, 4
mmol) in water/THF/toluene (1:1:1) 15 mL were stirred under argon for 5 min and
IPrꢀPEPPSI (0.05 g, 0.07 mmol) was added. Reaction mixture was refluxed at 85 °C
for 18 h. Silica gel column chromatography of crude compound afforded compound
as white solid. (0.17 g, 75%). M. P. 218 °C. FTIR (KBr, cmꢀ1):
6
ν
2925, 1612, 1549,
1
1405, 1322, 1184, 1102, 1064, 978, 948, 839, 792, 743, 705, 631, 614, 603, 542. H
NMR (500 MHz, CDCl3): δ 8.60 (s, 1H), 8.30 (s, 1H), 8.12 (d, 2H,
J = 8.2 Hz), 7.67ꢀ
13
7.75 (m, 5H), 7.56ꢀ7.60 (m, 5H), 7.45 (d, 2H,
J = 6.3 Hz) ppm. C NMR (500 MHz,
CDCl3): δ 143.82, 138.92, 131.69, 130.17, 129.84, 128.32, 127.56, 126.97, 126.16,
125.88, 124.96, 123.02 ppm. MALDIꢀTOF mass calcd. for C28H16F6 (M+H)+: 466.11;
found: 465.97 (M+).
Methods for micro/nano assemblies formation: The plate shape
5 microcrystals
were prepared by adding 0.5 mL of 0.5 mM /THF solution into 4 mL water
5
containing PVP (0.5 mg/mL) with a strong stirring. After stirring for 10 min, the
solution was kept undisturbed overnight at room temperature before characterization.
When PVP was replaced by CTAB and other conditions kept same, nanowires rather
14

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than microplates were produced. The preparation of SEM samples: An aliquot (20ꢁL)
of the solution was put on a silica wafer and dried over 24 h.
Supporting Information
NMR, mass spectra, absorption and emission spectra and differential pulse voltammograms
of compounds 1ꢀ6.
Acknowledgements:
We thank, Centre for Excellence in Basic Sciences, Mumbai for providing research
facilities. Partial funding was provided by Department of Science and Technology,
India (SR/FT/CSꢀ87/2010). We thank, Tata Institute of Fundamental Research,
Mumbai for providing the NMR and mass facility. We also thank National Centre for
Nanoscience and Nanotechnology, University of Mumbai and Bhabha Atomic
Research Center, Mumbai for for SEM and TCSPC facilities.
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Legends
Scheme 1: Literature methods used to synthesize aryl substituted anthracene
Scheme 2: Synthesis of anthracene derivatives 1ꢀ6
Table 1. Photophysical data for compounds 1ꢀ6.
Table 2. Electrochemical data for compounds 1ꢀ6.
Figure 1: 1H NMR of 1,8ꢀ(4ꢀfluorophenyl) anthracene, 5 in CDCl3.
Figure 2:Absorption (above) and emission (below) spectra of compounds 1ꢀ6 recorded in
toluene.
Figure 3: Cyclic voltammograms of 1ꢀ6 (except for 3) with ferrocene in CH3CN.
Figure 4: SEM images of different morphologies of 5 dissolved in THF/surfactant/water. A)
Rectangular plate like shape for 5 in PVP as surfactant, inset is a magnified area. B)
nanowires for 5 in CTAB as surfactants, inset is a magnified area.
Figure 5: Absorption and emission spectra of micro/nano assemblies of
5 in PVP,
CTAB and THF surfactants.
Figure 6: Optimized geometries of dimers of
1 (A) and 5 (B) and tetramer of 5 (C).
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O
O
OH
OH
Reduction
OTf
(a)
HO
HO
TfO
S-M coupling
Cl
O
O
Cl
Cl
Cl
PhMgX
Ni(acac)2
Zn/NH3, H2O
HCl
(b)
Scheme 1:
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Cl
O
O
Cl
Cl
Cl
Aryl boronic acid
Pr-PEPPSI-IPr
Ar
Ar
Zn/NH3, H2O
HCl
Na CO , 85 C
2
3
Toluene/water/THF
7
1-6
OCH3
COCH3
F
CF3
Ar =
1
2
3
4
5
6
Scheme 2
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Table 1
Comp
λabs (nm)b
τ (ns)a
λabs (nm)a
λem (nm)a
Φc
371, 392
375, 396
371, 390
379, 399
369, 387
374, 394
374, 394
ꢀ
404, 425
416, 432
410, 432
419, 440
431
0.95
0.75
0.71
0.65
0.45
0.72
0.67
0.93
3.54
3.60
DPA
381, 401
373, 393
391, 416
378, 400
382, 405
1
2
3
4
5
6
2.58
3.79
3.75
409, 431
410, 432
376, 397
b
c
a In toluene; in drop casted thin film; Relative quantum yields were calculated using 9,10ꢀDPA as
reference (Ethanol, ϕ = 0.95);
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Table 2
Eox
(V)
aEg
(eV)
bEHOMO
(eV)
cELUMO
(eV)
Comp
1.22
1.32
1.26
nd
ꢀ
ꢀ
ꢀ
DPA
ꢀ2.92
ꢀ2.94
ꢀ2.83
ꢀ2.86
ꢀ2.92
ꢀ2.93
ꢀ5.63
ꢀ5.62
ꢀ
ꢀ2.71
ꢀ2.68
ꢀ
1
2
3
4
5
6
1.34
1.30
1.32
ꢀ5.71
ꢀ5.66
ꢀ5.68
ꢀ2.85
ꢀ2.74
ꢀ2.75
b
aOptical band gap, calculated from absorption spectrum recorded in dropꢀcasted films; EHOMO
calculated from oxidation potentials (vs ferrocene) i.e. EHOMO = ꢀ (ꢀox w.r.t. Fc/Fc+ + 4.8 eV); cELUMO
= EHOMO ꢀ Eg; nd = not detected
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F
F
8.50
8.00
7.50
ppm (t1)
Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
29